The table saw is an apparatus in general use for making cuts in a wood workpiece. The table saw conventionally consists of a flat table-like work surface upon which the workpiece rests and a powered, rotating circular saw blade mounted in such a manner that the blade may be raised to project upwardly through a slot in the work surface. The table saw operator can then make cuts in the workpiece by moving the workpiece over the work surface to engage the saw blade.
Typically, a table saw is equipped to accept a variety of blades which are suitable for performing differing cuts in a workpiece. For example, most table saws are equipped to allow the interchange of at least a saw blade for cutting a workpiece in two, and a dado blade for making a grooved cut in a workpiece.
In order to accommodate the various blades, however, it is also necessary to provide a means to furnish a different slot in the work surface for each blade due to the differing cross-sectional shape of the blades. Only a very wide slot in the work surface would accommodate all types of blades, and such a slot would not adequately support the workpiece near the blade. Many such slotting arrangements are known.
One conventional solution is to instead provide a recessed opening in the work surface in which a throat plate, having the correctly shaped slot for the blade being used, may be mounted. When mounted in the recessed opening, the throat plate forms a planar surface with the work surface and provides a slot through which the blade may be projected. By changing the throat plate whenever the blade is changed, an appropriately shaped slot for each blade is furnished. These throat plates are conventionally made of metal.
One disadvantage of the conventional throat plate arrangement is that the slots in the metal plates are usually of substantially greater width than the blade to avoid contact between the plate and the teeth of the blade. However, because the workpiece supported on the work surface is not supported adjacent to the blade edge, rough cutting of the work may result.
Maier, et al, U.S. Pat. No. 4,543,866, discloses a slotting arrangement in which a metal cover plate is provided having a slot of sufficient dimensions to accommodate blades of different designs and prevent contact between the cover plate and the blade when in operation. The cover plate is provided with teeth for positioning and locking the cover plate in a base plate which serves as a work surface of a table saw. This arrangement has the same disadvantages as the conventional throat plate arrangement. Substantial clearance between the cover plate and the blade is maintained, resulting in rough cutting of a workpiece.
Mendelsohn, U.S. Pat. No. 4,161,900, discloses a veneer edging jig consisting of an upper and lower clamp plate for gripping a stack of veneer sheets therebetween such that a portion of the veneer sheets projects outwardly from matching edges of the clamp plates. The clamp plates are made of metal with their matching edges formed of wood. The portion of the veneer sheets may be cut by first, placing the jig and veneer sheets on a standard table saw having a flat table surface and vertical circular saw blade projecting through a slot therein. The matching edges of the jig plates are then aligned longitudinally with the saw blade before moving the plates over the table surface with the matching edges flush against the blade. In this manner, the workpiece is supported adjacent to the blade during a cutting operation without changing the conventional throat plate slotting arrangement. A disadvantage of the edging jig arrangement, however, is the bulk of the apparatus and the need to install it on a workpiece before each cut.
In Gustin, U.S. Pat. No. 2,709,463, an apparatus for forming slots in a wood well cover is disclosed. The well cover is adapted for mounting in a well opening in a work surface of a table saw with the cover resting upon a lip around the opening such that the upper surface of the cover is flush with the work surface. The table saw has a plurality of saw blades rotatably mounted on a mandrel having a stationary axis, with the saw blades projecting vertically through the well opening. The invention consists of a frame mounted to the work surface with hinges to lower the cover over the rotating blades, into the well opening, thereby cutting slots in the cover.
A slot apparatus consisting of a slotted wood well cover, like that disclosed by Gustin, features minimal clearance slots for supporting a workpiece near a saw blade. One drawback to such an apparatus is that the saw operator must expend considerable time and labor to form well covers of the correct dimensions to fit the well opening. A further disadvantage is that such an arrangement may result in considerable waste of wood since an entire wood well cover must be made for each saw blade combination used with the table saw. Also, the wood well cover, as compared to a metal throat plate, is subject to more wear in use and is more difficult to fashion to precise tolerances for fitting snugly in a well opening. Therefore, the wood well cover is more prone to lateral movement within the well opening when subjected to working conditions.